1. Field
The present disclosure relates to a rubber composition for the manufacture of an air-impermeable tire inner layer, commonly known as a tire “inner liner”.
2. Description of Related Art
Tubeless tires have an inner surface of low air permeability so as to prevent the tire from deflating and to protect the sensitive internal regions of said tire from the ingress of oxygen and water, such as the plies containing oxidation-sensitive metal cords, this protectio, improving the endurance of the tire. At the present time, such protection of the inner surface of tires is generally achieved by inner liners consisting of elastomeric compositions based on butyl rubber. However, the air impermeability performance of butyl rubbers is linked to a not inconsiderable minimum thickness (of the order of a millimetre) and therefore to a certain weight, which does not make it possible to efficiently meet these new requirements.
Thus, it is necessary to add reinforcing fillers, such as carbon black, to the elastomeric inner liner composition in order to improve its impermeability. However, in large quantities, these reinforcing fillers impair certain properties of the composition both in the uncured state: difficulty in processing the uncured composition, commonly referred to as a “processability” difficulty, and in the cured state: degradation of mechanical properties, especially reduction in the flexural strength. The introduction of plasticizers of the oil type makes it possible to overcome these processing and mechanical property aspects but is highly detrimental to the impermeability of the inner liner.
Various solutions have been envisaged for overcoming these drawbacks, in particular by using other types of fillers, often known as smectites, to be added to the reinforcing fillers. These organophilic smectites improve the impermeability properties of the materials if they are well dispersed in the material.
The publication WO 2006/047509 by the Applicant describes a composition for a tire inner liner, the composition of which, based on predominantly diene rubber and comprising carbon black, comprises non-reinforcing fillers consisting of organophilic smectites that reduce the permeability to gases, dispersed in the elastomeric matrix and also a specific plasticizer consisting of a terpene resin having in particular a glass transition temperature Tg of greater than 50° C. This composition effectively exhibits mechanical and impermeability properties which render it acceptable for use as a tire inner liner, by virtue of the combined effect of these organophilic smectites and this high Tg resin.
Application WO 2008/145314 describes a rubber composition for a tire inner liner based on at least a butyl rubber, a reinforcing filler, graphite and a plasticizing hydrocarbon resin, which possesses processability and flexural strength properties that are as good as the compositions from the prior art, and improved gas impermeability properties, and which also makes it possible to significantly improve the rolling resistance and endurance properties.